talking about today
I’ll let to be excuses speak for that
just finish the last video enjoy your
vacation why thank you I did very much
observe my slightly more tan face and
since you’re asking for suggestions
how about closures to be us losers it is
in case you’re a noob you are dropping
by this is a series where we learn
functional programming using javascript
you can watch the other episodes in this
series by clicking there so what are
closures in JavaScript functions are not
just functions they are also closures
what that means is that the function
body has access to variables that are
defined outside the function let me show
you have a look at this code we are
assigning a variable here I called me
and we’re assigning in the value Bruce
Wayne and we’re then learning function
or greet me which console logs hello me
exclamation mark and then we call read
function here let’s run that hello Bruce
way notice that we are not passing in an
argument here we’re just calling it
without any arguments we are directly
referring to the me that is assigned
outside of the function scope the reason
that we can do this is that JavaScript
functions like Whitney or closures we
cannot do this in languages that does
not have support for closures in the
language without support for closures we
would have to pass the name
and argument the function instead
because such a language does not have
access to the the outer scope of itself
like that let me go back to the original
I really like to stress here that greet
me does really have access to the outer
variable scope it does not snapshot the
value of me at the time it is declared
for instance if I reassign me to be
Batman here and run it it will say hello
Batman so greet me does not copy the
value of me it actually reads whatever
the variable is at that time from the
outer scope and it will do this even if
greet me was and a synchronous function
being called from I’ll say an AJAX call
back or something like that greet me
will remember this outer context that
it’s declaring even if greet me is
called from a completely different part
of the application or a different module
it will still refer to this specific
context you all being healthy skeptics
you’re probably now asking yourself why
is this useful what is the point of
closures closures actually have quite a
bit of use cases but I’m going to give
you one that I think illustrates why
closures are useful let’s look at this
function together it’s called send
requests and we start by assigning a
request ID to a variable we then use
just a yin stand a jQuery AJAX function
we call an Earl and when that is
successful we alert the string request
request ID protect I’m not gonna run
this I’m gonna let your imaginations
execute it but what will happen is that
since all functions in JavaScript or
closures including the callback to
it will have access to the request ID
that we flared even though this callback
is executed way later this really
illustrates a good use of closures it’s
when you start a task and you want to
specify something that happens when that
task is done with stuff that is
available to you when you start the task
closures makes that easy and readable in
a language that does not support
closures you would probably have to have
some kind of data object that you passed
into the Ajax function which it in turn
passed into success and if it didn’t
have that you would probably have to
create some kind of request objects with
properties and stuff instead of just
simply doing function this kind of thing
becomes sort of a key if you don’t have
closures we have talked a bit about what
closures are I have showed you a
practical example of why they are a good
thing but closures is one of those
things in JavaScript that this permeates
the entire language there are more use
cases than the one I showed you more
than will fit into this video or even a
second one closures is just one of those
things that you have to use a lot on
your own in your code for you to really
internalize it
however Mozilla having just writes
JavaScript documentation overall has a
super super good page on closures on
their side and I have linked it down in
the show notes you should go there and
check those examples out and start using
closures in your code to get a feel for
it and that is it for today as usual I’d
love to hear from you
either down below or at mpj me on
tell me what you thought about this
episode or ask me a random question or
maybe tell me what you think that the
next episode Monday should be about and
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